ABSTRACT

Context The prevalence and distribution of gonococcal and chlamydial infections
in the general population are poorly understood. Development of nucleic acid
amplification tests, such as the ligase chain reaction assay, provides new
opportunities to estimate the prevalence of untreated infections in the population.

Objective To estimate the overall prevalence of untreated gonococcal and chlamydial
infections and to describe patterns of infection within specific demographic
subgroups of the young adult population in Baltimore, Md.

Design and Setting Cross-sectional behavioral survey based on a probability sample of Baltimore
households with collection of urine specimens between January 1997 and September
1998.

Participants A total of 728 adults aged 18 to 35 years completed the interview portion
of the study, and 579 of these respondents also provided a urine specimen
adequate for testing.

Main Outcome Measure Prevalence of untreated infection, as measured by the percentage of
specimens testing positive for gonococcal and chlamydial infection by ligase
chain reaction, weighted to reflect variations in probabilities of sample
selection from the population. Alternate estimates of the prevalence of recent
treated infection were derived from clinically diagnosed cases reported to
the Baltimore City Health Department and by diagnoses reported by participants
in the survey.

Results An estimated 5.3% (SE, 1.4%) of the population aged 18 to 35 years has
an untreated gonococcal infection, and 3.0% (SE, 0.8%) is estimated to have
an untreated chlamydial infection. While 7.9% (SE, 1.6%) of the population
is estimated to have either an untreated gonococcal or chlamydial infection,
estimated prevalence is substantially higher among black women (15.0%; SE,
3.7%). Few participants with untreated infections reported dysuria or discharge
during the 6 months preceding testing. The estimated number of untreated gonococcal
infections in the population (9241; SE, 2441) substantially exceeds both the
number of such infections diagnosed among Baltimore adults aged 18 to 35 years
and reported to the Baltimore City Health Department during 1998 (4566), and
the estimated number of diagnoses derived using participants' reports for
the 12 months prior to the survey (4708 [SE, 1918] to 5231 [SE, 2092]). The
estimated number of untreated chlamydial infections (5231; SE, 1395) is also
greater than the number of cases reported to the health department in 1998
(3664) but is slightly less than the estimated number of diagnoses derived
using participants' reports of chlamydial infections diagnosed during the
12 months prior to the survey (5580 [SE, 1918] to 6975 [SE, 2441]).

Conclusion In 1997-1998, the estimated number of undiagnosed gonococcal and chlamydial
infections prevalent in the population of Baltimore adults aged 18 to 35 years
approached or exceeded the number of infections that were diagnosed and treated
annually.

Untreated infection with Neisseria gonorrhoeae
or Chlamydia trachomatis can result in chronic pelvic
pain, infertility, and potentially fatal ectopic pregnancies among women.
In addition, these bacterial sexually transmitted diseases (STDs) serve as
biological cofactors that facilitate transmission of human immunodeficiency
virus (HIV). Untreated chlamydial infections, for example, are estimated to
increase the likelihood of HIV transmission by a factor of 1.4 to 3.3.1- 3

Unfortunately, the prevalence and distribution of these STDs within
the population are poorly understood. Until recently, our knowledge was limited
by its exclusive dependence on 2 data sources with well-recognized inadequacies—the
counting of infections reported to public health departments and studies of
convenience samples of special populations, such as clinic patients. While
these sources can provide useful information, they are inherently incapable
of characterizing untreated STD infection in the population at large. This
problem is particularly severe for infections whose symptoms are mild or nonexistent.
Available evidence suggests that a substantial fraction of gonococcal and
chlamydial infections are asymptomatic.4- 8
The Institute of Medicine has noted,8 such
STDs spawn " . . . hidden epidemics of tremendous health and economic consequence
in the United States . . . [T]he scope, impact, and consequences of [these]
STDs are underrecognized by the public and health care professionals."

The recent development of nucleic acid amplification tests (NAATs) for
the diagnosis of gonococcal and chlamydial infections using urine specimens
has generated new models for research on the epidemiology of these STDs.9- 11 Since the urine specimens
required for NAAT can be obtained in population surveys, generalizations about
the prevalence and patterns of infection now can be derived from surveys of
probability samples of the general population rather than samples of clinic
patients or other special populations. This research model provides estimates
(with known margins of sampling error) for the prevalence of untreated infections
both in the population at large and in identifiable subpopulations.

To provide a more accurate understanding of the hidden epidemics of
untreated infection with N gonorrhoeae and C trachomatis, using probability sampling methods, we recruited
a population sample of young adults aged 18 to 45 years to participate in
a survey of sexual and other sensitive behaviors and STD history. We then
used NAATs of urine specimens obtained from survey respondents aged 18 to
35 years to detect the presence of untreated gonococcal and chlamydial infections.
The resultant data allowed us to estimate the prevalence and patterns of untreated
infection in our target population, adults aged 18 to 35 years in Baltimore,
Md.

METHODS

Sample Design

The sample for the Baltimore STD and Behavior Survey was drawn from
households residing within the municipal boundaries of the city of Baltimore
(1998 population: 645 664).12 Households
were selected using a stratified probability sampling design that selected
residences from the Baltimore Real Estate Property Registry. This registry
includes all properties—both taxable and tax-exempt—within the
city of Baltimore. Two sample strata were disproportionately sampled to ensure
adequate representation of (1) young black men and (2) young adults living
in predominantly white US Census tracts with elevated levels of STDs (based
on Baltimore City Health Department [BCHD] STD surveillance statistics). Operationally,
these 2 strata comprised (1) households with an age-eligible man drawn from
census tracts with 95% to 100% black residents according to the 1990 US Census;
and (2) adults aged 18 to 35 years residing in 13 census tracts that had the
highest rates of reported gonococcal infection among tracts with 0% to 9%
black residents. A third crosscutting sample stratum was created to accommodate
the refielding of a 50% random subsample of cases for which our quality control
procedures could not verify the integrity of the interview data (see below).

This sample design oversampled segments of the population that are known
to have higher rates of STDs (ie, young black men and whites living in US
Census tracts with high rates of reported STDs). Oversampling is routinely
used in household surveys to ensure adequate sample sizes for difficult-to-survey
or numerically rare segments of the population. Probability sampling requires
that every member of the population have a nonzero probability of selection.
Complex probability samples use stratification and sampling at different rates
in the design stage and sample weighting (by the inverse of the sampling probabilities)
at the analysis stage to yield samples representative of the targeted population.
Our prevalence estimation uses sampling weights to adjust for the unequal
probabilities of selection across sample strata.

Informed Consent

A 2-stage procedure was used to obtain informed consent. Informed consent
(both oral and written) was first obtained from all survey participants (aged
18-45 years) prior to the survey interview. A separate consent (both oral
and written) was obtained from respondents (aged 18-35 years) participating
in the urine testing. The informed consent process made explicit that the
urine would not be used for drug testing and that, in compliance with state
laws, specimens found positive for gonococcal and/or chlamydial infection
would be reported to the BCHD. The protocol for this study was approved by
institutional review boards at the Research Triangle Institute and Johns Hopkins
Medical Institutions.

Interview

Respondents completed a detailed survey on sexual behavior, prior STD
history, STD symptoms, drug and alcohol use, social attitudes and behaviors,
and individual background characteristics. Interview data were collected by
36 trained interviewers in the respondent's home. Interviewers were instructed
to conduct the interviews in a private place in the home or at an alternate
location where privacy could be ensured. They were specifically instructed
that they could not conduct an interview if another person was listening.
To satisfy another objective of the research program, respondents were randomly
assigned to complete the survey questionnaire using either traditional survey
procedures (ie, computer-assisted personal interview with some paper-and-pencil
self-administered questionnaires) or an audio computer-assisted self-interviewing
technology.13- 15
(Random assignment of respondents to interview modes ensures that there will
be no systematic association between interview mode and the variable of central
interest to us —NAAT-diagnosed gonococcal or chlamydial infection.)
Data from these 2 interview modes are aggregated in this article. The survey
took an average of 26 minutes to complete. Respondents received $10 to $20
at the conclusion of the interview.

Collection and Processing of Urine Specimen

At the conclusion of the interview, participants aged 18 to 35 years
were asked to provide a urine specimen for testing. Respondents who agreed
to provide a urine sample for screening received an additional $10 to $20.

N gonorrhoeae and C trachomatis were detected in urine specimens using a ligase chain reaction (LCR)
assay (Abbott Laboratories, North Chicago, Ill). The LCR assay was performed
according to the manufacturer's instructions. Positive test results were reconfirmed
by a repeat analysis using this same procedure. If this second analysis was
negative, the case was coded as negative. (Repeat analyses were not available
for 3 cases that tested positive on initial testing. These cases were coded
positive based on their initial testing.)

Notification of Results

All respondents were given a telephone number they could call to learn
of their test results, and study staff used a succession of methods to attempt
to contact participants who tested positive (telephone, registered letter,
and, if refused or undelivered, regular mail). Free, expedited treatment at
one of the BCHD clinics was offered to all contacted subjects who tested positive.

Quality Control

During the course of the study, a subset of interviewers' work was subject
to independent verification to confirm that the interview had been completed
and that a urine specimen had been requested if the respondent was 35 years
or younger. A verification interviewer (not part of the regular survey staff)
contacted the household to confirm the respondent's name, participation in
the survey, demographic information, date of interview, whether a urine specimen
had been collected, and whether the respondent had been paid the monetary
incentive. This procedure identified 7 interviewers who appeared to have fabricated
some of their interviews or to have collected interview data and urine specimens
from households other than those selected into the sample. All of the interviews
submitted by these interviewers were subject to verification, and data were
retained only if the verification result was positive. (A full account of
these procedures has been presented elsewhere.16)

Over the course of the study, 56% of all completed survey interviews
included in the final database were subject to independent verification.

Statistical Analyses

Prevalence estimates were derived using case weights that are inversely
proportional to the probabilities of case selection and that incorporate a
poststratification weighting to ensure that the sample distribution matched
the 1997 US Census tabulation of the Baltimore population by race, sex, and
age. Statistical algorithms that take account of the impact of complex sample
designs on variance estimates, as implemented in the survey data component
of Stata 6.0,17,18 were used in
all analyses and calculation of variance estimates. We tabulated frequencies
of demographic characteristics to obtain a descriptive profile of the sample.
Logistic regression and χ2 tests were used to assess the association
between estimates of infection status and other subject characteristics. Tests
of the equivalence of prevalence estimates for gonoccocal vs chlamydial infections
take account of the covariance that arises when estimates are derived using
measurements made on the same subjects.

Impact of Assay Performance on Estimated Prevalence

To assess the potential impact of assay performance on prevalence estimates,
sensitivity analyses were conducted using a plausible range of estimates for
the specificity (0.990-0.999) and sensitivity (0.90-0.94) of the LCR assays
used in this research. Past research indicates that NAAT assays have high
sensitivity (>0.90) and specificity (>0.99) for the detection of chlamydial
and gonococcal infections because genetic material from the target organisms
is detected.19- 24
In the present study, specificity was optimized by retesting almost all positive
specimens and considering a specimen positive only if both initial and repeat
test results were positive. Sensitivity analyses were performed using spreadsheets
constructed in Excel 2000 (Microsoft, Redmond, Wash).

Impact of Missing Data on Estimated Prevalence

To assess the impact of respondents' refusal or inability to provide
urine specimens on our prevalence estimates, we used logistic regression to
model the likelihood that respondents would test positive for either gonococcal
or chlamydial infection based on a range of sociodemographic and behavioral
variables collected in the survey interview. This model was estimated using
data from those respondents who provided urine samples adequate for testing.
The parameter estimates derived for this model were then used to impute the
probability that individual nonrespondents in the urine collection would have
tested positive for either pathogen had they been tested. These imputed probability
values for respondents who did not provide a urine specimen were combined
with the actual gonococcal and chlamydial infection test results for respondents
who did provide specimens. The synthetic estimate derived by this imputation
process (8.1% for infection with C trachomatis and/or N gonorrhoeae) was quite similar to the unadjusted estimate
derived from tested specimens alone (7.9%). Since imputation for nonresponse
did not have a substantial effect on the overall prevalence estimate, we used
unadjusted estimates based on complete data in our analyses.

Other Data Sources

In addition to prevalence estimates derived from LCR testing of urine
specimens, we derived alternate prevalence estimates from physician- and laboratory-diagnosed
cases of gonococcal and chlamydial infection reported to the BCHD in 1998
(G. Olthoff, MHA, written communication, November 2, 2001). Health Department
estimates are derived from the Baltimore STD reporting system and eliminate
instances (as duplicate reports) in which infection with the same pathogen
is reported in the same individual 2 (or more) times within a 30-day period
(W. Braithwaite, BA, written communication, December 5, 2001). Reports of
infection of the same individual outside of this 30-day period are included
in the case counts.

Alternate prevalence estimates were also derived from survey respondents'
answers to questions asking whether they had ever heard of gonorrhea and chlamydia
and, if so, had they been diagnosed as having these infections in the 12 months
prior to the survey. Respondents' answers provide 2 estimates of the prevalence
of diagnosed infection. The first and lower estimate assumes that respondents
who had not heard of a disease (gonorrhea or chlamydia) had not been diagnosed
as having the disease in the previous 12 months. A second and higher estimate
assumes that persons who had never heard of the infection were just as likely
to have been diagnosed as having this infection in the past 12 months as respondents
who had heard of the infection.

For both diagnoses reported to the BCHD and those reported by survey
respondents, we assume that diagnosis is accompanied by treatment, although
in a small but unknown number of cases this may not be true.

RESULTS

Survey Execution

Of the 3182 households selected for interview, 2727 (85.7%) were successfully
screened. Screening identified a total of 1224 English-speaking adults who
were between the ages of 18 and 45 years and eligible for interview. Survey
interviews were completed with 1014 respondents (82.8%) between January 1997
and September 1998.

The protocol specified that only respondents between the ages of 18
and 35 years were eligible to provide urine for gonorrhea and chlamydia testing.
Of the 1014 respondents between the ages of 18 and 45 years who completed
the interview, 728 respondents aged 18 to 35 years were asked to provide urine
for testing. Of the 728 age-eligible respondents, 579 (79.5%) provided a urine
specimen adequate for testing, 119 (16.3%) refused to provide a urine specimen,
and 30 (4.1%) were not tested because of inadequate urine volume, interviewer
error, or other logistical problems. Table
1 presents the unweighted numbers of adults providing urine samples
and weighted percentage distributions for selected sociodemographic groups.

Estimated Prevalence of Untreated Infections

Among Baltimore adults aged 18 to 35 years, we estimate the prevalence
of untreated chlamydial infection is 3.0% (SE, 0.8%) and the prevalence of
untreated gonococcal infection is 5.3% (SE, 1.4%) (Table 2). Overall, 0.4% (SE, 0.3%) of adults are estimated to have
both infections (data not shown), and 7.9% (SE, 1.6%) of Baltimore adults
aged 18 to 35 years are estimated to have either gonococcal or chlamydial
infection (or both). The difference between the estimated prevalence of these
2 infections is not statistically significant (P
= .16). All respondents who reported a diagnosis of gonococcal (unweighted
sample of 9) or chlamydial (unweighted sample of 13) infection in the past
12 months tested negative by LCR for the diagnosed (and presumably treated)
pathogen.

Table 2 includes both weighted
population prevalence estimates and unweighted counts of the numbers of infections
detected and subjects tested. The unweighted sample counts represent the results
of our NAAT analysis; they do not provide valid estimates of the prevalence
of infection in the population as a whole or in any subpopulation. Since we
used a complex sample design that purposely oversampled certain segments of
the population (see above), only the weighted estimates can be used to make
inferences about the prevalence of NAAT-detectable infections in the population.

Impact of Assay Performance on Estimated Prevalence

Assuming the sensitivity of the LCR assay was 0.90 to 0.94 and specificity
was 0.990 to 0.999, sensitivity analysis indicates that the "true" underlying
prevalence of chlamydial infection would be 2.2% to 3.2%, given our population
prevalence estimate of 3.0%. For gonorrhea, the "true" underlying prevalence
would be 4.6% to 5.8%, given our population prevalence estimate of 5.3%. This
sensitivity analysis suggests that our prevalence estimates are not substantially
affected by the imperfection of the LCR assay.

Untreated Infections by Sex, Race, and Age

The prevalence of gonococcal and chlamydial infections varies substantially
across subpopulations (Table 2).
We estimate that 15.0% (SE, 3.7%) of black women have gonococcal and/or chlamydial
infections while the estimated infection rates are significantly lower for
black men (6.4% [SE, 2.1%]; P = .02) and nonblack
women (1.3% [SE, 0.5%]; P<.001). Estimated prevalence
was lower among nonblack men (2.8% [SE, 1.3%]) than among black men, although
the difference was not significant. For both blacks and for women, gonococcal
infection appears to be more prevalent than chlamydial infection, but this
difference is also not statistically significant.

Table 3 shows a significant
decline with age in the estimated prevalence of NAAT-detectable chlamydial
infections (P = .006 for trend) and subjects' reports
of diagnoses of gonococcal infections during the past 12 months (P = .02 for trend). A parallel, although less uniform and nonsignificant,
trend occurs for chlamydial infections diagnosed in the past year.

Current untreated gonococcal infections show a different pattern. The
highest prevalence of detectable gonococcal infection (10.2% [SE, 3.3%]) occurs
among persons aged 31 to 35 years. While the number of infections detected
is small (unweighted counts: 33/579 [aged 18-35 years] and 17/207 [aged 31-35
years]), the unexpectedly high prevalence estimated for gonococcal infection
among older respondents is unlikely to be due to the small sample sizes. (The
null hypothesis that the population prevalence of gonococcal infections is
equivalent among adults aged 31 to 35 years and those aged 18 to 30 years
is rejected with P<.001.) High estimated prevalences
of untreated gonococcal infections are observed among both men (7.8%) and
women (12.2%) in the group aged 31 to 35 years (data not shown).

Symptoms and Antibiotic Use

The high prevalence of untreated infections estimated for the Baltimore
population raises questions about the reasons why medical diagnosis and treatment
were not obtained. Interview data indicate that symptoms were rarely reported
among persons with untreated gonococcal or chlamydial infections. Excluding
persons receiving treatment for a gonococcal or chlamydial infection in the
previous 6 months, only 2.0% of currently infected respondents reported dysuria
(burning on urination) and 4.7% reported discharge within the past 6 months.
Untreated infections were found less frequently among persons reporting dysuria
during the preceding 6 months than among those who did not report this symptom
(prevalence: 2.0% vs 8.8% [odds ratio {OR}, 0.21]; P
= .08). Similarly, infections were less likely to be reported among persons
who report dripping or discharge in the past 6 months than among those who
did not, but this difference did not approach statistical significance (4.7%
vs 8.4% [OR, 0.54]; P = .43).

Persons who reported antibiotic use in the 6 months prior to testing
were less likely to test positive for gonococcal and/or chlamydial infection
than those who reported no antibiotic use in this period (4.4% vs 10.5% [OR,
0.40]; P = .04). In theory, variation in the use
of antibiotics could produce a negative association between symptom reporting
and current infection status if antibiotics were administered presumptively
on the reporting of dysuria or discharge. To control for this possibility,
we examined the relationship of symptoms and current infection status in persons
reporting no antibiotic use and no diagnosed gonococcal or chlamydial infections
in the 6 months prior to testing. A trend toward asymptomatic infection remains
(OR, 0.24 for dysuria; and OR, 0.32 for discharge), however, with the diminished
sample sizes, these results are not statistically significant (P = .19 and P = .30, respectively).

Number of Treated vs Untreated Infections

Overall, 4566 gonococcal infections were diagnosed in persons aged 18
to 35 years and reported to the BCHD in 1998 (Table 4). This would represent a maximum population prevalence of
2.6% (under the assumption that no person had ≥2 infections recorded during
the year). Interview data provided by our survey respondents suggest that
between 4708 (2.7%) and 5231 (3.0%) individuals in this age group were diagnosed
as having (and presumably received treatment for) gonococcal infections in
the 12 months prior to our survey. Based on NAAT assays of urine specimens,
we estimate that 9241 (5.3%) of this age group had a current and untreated
gonococcal infection at the time of our survey. The divergence in estimates
of diagnosed and undiagnosed gonococcal infections is most striking for women.
Three estimates of the number of women (aged 18-35 years) diagnosed as having
gonococcal infection annually in Baltimore lie in the range of 1272 (1.4%)
to 2051 (2.3%). NAAT analysis of urine specimens from our probability sample
of this population leads us to estimate that 6087 women (6.7%) were carrying
an undiagnosed gonococcal infection at the time of the survey.

For chlamydial infection, BCHD records indicate that 3664 infections
were diagnosed in this age group in 1998. This represents a maximum prevalence
of 2.1%. Responses during the survey interview suggest that 5580 (3.2%) to
6975 (4.0%) of the population were diagnosed as having and presumably treated
for chlamydial infections in the 12 months prior to our survey. Testing of
urine specimens yields an estimate that 5231 (3.0%) of this age group had
a current and untreated chlamydial infection. Examination of the results by
sex indicates that only 391 men (0.5%) were diagnosed as having chlamydial
infections and reported to the BCHD in 1998 while our testing of urine specimens
yields an estimate that 1336 men in this age group (1.6%) had a current untreated
chlamydial infection. Male respondents reported diagnoses of chlamydial infection
by their health care providers at rates that are considerably higher than
recorded in BCHD statistics (1.9%-2.5% vs 0.5%). This may reflect presumptive
treatment (eg, for nongonococcal urethritis) without diagnostic testing.

COMMENT

The foregoing estimates indicate that nearly 1 in 12 (7.9%) Baltimore
adults between the ages of 18 and 35 years has an untreated infection with
either N gonorrhoeae or C trachomatis. The estimated prevalence for black women is greater than 1 in 7 (15.0%).
Two important conclusions emerge when these estimates, which represent undiagnosed
infections prevalent in the population, are compared with estimates of the
number of infections diagnosed annually. First, the combined number of gonococcal
and chlamydial infections that persist undiagnosed and untreated in this population
exceeds the number of infections that are diagnosed and treated in a given
year. Second, there appears to be a large reservoir of undiagnosed gonococcal
infections in Baltimore, particularly among women.

It is impossible to know the duration of the infections detected in
this study. We note, however, that nearly all of the detected infections occurred
among adults who reported no recent symptoms. In addition, elevated levels
of gonococcal infection were detected among older adults aged 31 to 35 years.
The lack of symptoms and high levels of gonococcal infection among the oldest
sampled age group suggest that persistent infections may be responsible for
the high prevalence of untreated asymptomatic infections detected in this
study. Longstanding infections may represent low organism burden, partial
immunological clearance,26 or infection with
organism strains that cause less symptomatic disease.27
In some cases, these persistent asymptomatic infections may be associated
with significant sequelae, such as infertility. In other cases, the clinical
importance and transmissibility of these infections is less clear.28 Although there is some uncertainty about the interpretation
of NAAT-detected infections, we believe our findings have 2 important implications.

First, prompt consideration should be given to strategies for improving
the diagnosis and treatment of asymptomatic infections in this population.
The urine-based NAAT assays used in this research are approved by the Food
and Drug Administration for diagnosis of gonococcal and chlamydial infections.
As such, we believe it is prudent to plan appropriate public health actions
in response to the high prevalence rates we have detected. Strategies for
reducing the prevalence of infection in this population might include screening
or routine testing in health care settings for the entire population of young
adults, including persons who formerly would be considered to be at low risk
of infection. (Such efforts will require confronting issues that are beyond
the scope of the present article, including identification of appropriate
methods for delivering and financing such testing, and the role to be played
by public health facilities and private health care providers.)

In support of this recommendation, we note that Mehta et al29 recently reported testing 454 patients (aged 18-31
years) seeking medical care for reasons other than STD symptoms at the adult
emergency department at Johns Hopkins Hospital and Health System (Baltimore,
Md). Using urine-based NAAT assays, investigators found that 9.3% of these
patients tested positive for chlamydial infection and 5.3% tested positive
for gonococcal infection. Their sample is not directly comparable with our
own since they recruited patients in a large Baltimore emergency department.
However, both our estimates and those of Mehta et al are derived from screening
adult populations outside of an STD care setting.

The second implication of our findings is that research is urgently
needed to improve our understanding of the clinical and public health significance
of NAAT-detectable infections. It is possible that NAAT assays are identifying
clinically inconsequential infections because of the assays' ability to detect
extremely low levels of viable organisms (ie, below the infectious inoculum)
or amplifiable DNA (or RNA) from residual pathogens (ie, nonviable organisms)
of past infections that are well on their way to being cleared. One potentially
informative line of research may be to compare the transmissibility and clinical
consequences of infections that are detectable only by NAAT assay vs those
that are detectable by traditional assays.30

In addition to its substantive findings, the present study provides
an example of the feasibility and benefits of combining population survey
techniques and NAAT analysis of urine specimens in research on the epidemiology
of STDs. Such research can complement and enrich the epidemiological insights
gained from studies using case reporting systems and studies of clinical and
other special populations. Most importantly, this research permits generalizations
about the prevalence in the population at large—or at least in that
fraction of the population who consents to being surveyed.

Interpretation of our research findings will benefit from replication.
Since teenagers both contract infections from and transmit infections to the
adult population, any replication should include this segment of the population.
Annual or biannual monitoring of STD prevalence using population survey techniques
in Baltimore and elsewhere could enrich our understanding of the epidemiology
of these STDs. It could also provide important guidance on the appropriate
roles of population prevalence data and STD case reports in tracking trends
in these STDs and identifying subpopulations that might benefit from screening
or other interventions designed to inhibit the spread of these infections.

Bureau of the Census. Population estimates for counties by age and sex: annual time series
July 1, 1990 to July 1, 1999 (CO-99-9). Washington, DC: Population Estimates Program, Population Division,
US Census Bureau; August 30, 2000. Available at: http://www.census.gov/population/estimates/county/cas/cas24.txt. Accessed December 4, 2001.

Bureau of the Census. Population estimates for counties by age and sex: annual time series
July 1, 1990 to July 1, 1999 (CO-99-9). Washington, DC: Population Estimates Program, Population Division,
US Census Bureau; August 30, 2000. Available at: http://www.census.gov/population/estimates/county/cas/cas24.txt. Accessed December 4, 2001.

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